Stencil printing process



Dec. 7, 1965 F. wElss STENCIL PRINTING PROCESS Filed April 11. 1962 FIGB INVENTOR' FRANZ WEISS ATT lYS United States Patent 3,221,648 STENCIL PRINTING PROCESS Franz Weiss, Park Ridge, Ill., assignor to Poster Products, Inc., Chicago, Ill., a corporation of Illinois Filed Apr. 11, 1962, Ser. No. 186,773 8 Claims. (Cl. lill- 129) This invention relates to a printing apparatus and process and more particularly to a printing apparatus and process especially suited for multi-color printing.

Many difficulties have heretofore been encountered in the multi-color printing of signs and advertising displays ,and the results obtained in such printing have left much to be desired because of the time required, the expense of the operation, and the quality of the product.

One of the objects of the present invention is to provide a new and improved process and apparatus for printing which is especially adapted to multi-color printing.

Another object of the invention is to provide a process and apparatus for printing in which several colors can be printed at the same time.

Still a further object of the invention is t-o provide a process and apparatus for printing in which high quality prints can be obtained in a relatively short period of time and with a minimum of expense.

An additional object of the invention is to provide a process and apparatus for printing in which the steps involved are simple and the apparatus requir'ed is relatively inexpensive.

Other objects and advantages of the invention will appear from the following description in conjunction with the accompanying drawing in which FIGURE 1 is a plan view with parts broken away of a printing apparatus provided in accordance with the inv'ention;

FIGURE 2 is a cross section taken along the line 2-2 of FIGURE 1; and

FIGURE 3 is a partial cross section taken along the line 3 3 of FIGURE 1.

In accordance with the invention a printing apparatus is provided which contains the following essential elements: (a) supporting means for supporting a porous sheet material; (b) a stencil screen frame; (c) a stencil screen having pervious portions extending across said frame; (d) means to form a fluid-tight space between said stencil screen and said porous sheet material when said stencil screen and said porous sheet material are brought into proximity to one another; (e) a coloring composition disposed on the pervious portions of said stencil screen on the side remote from said porous sheet material; (f) means to apply reduced pressure to the side of said porous sheet material remote from said screen, and (g) means to apply additional reduced pressure to the space between said stencil scre'en and said porous sheet material when said stencil screen and said porous sheet material are in such proximity as to provide a fluid-tight space.

The supporting means (a) is preferably generally convex in shape and has a series of holes therein communicating with a vacuum pump through a conduit controlled by a valve or other suitable m'eans. When a porous sheet material is placed on the supporting means (a) and the valve to the vacuum pump is opened, the sheet material is held in place by the reduced pressure created on its underside. Another series of holes is provided in the supporting means (a) beyond the margins of the porous sheet material and connected separately from the first series of holes through a pipe, conduit or the like, controlled by a valve or other suitable means to a source of reduced pressure which may be the same vacuum pump used in applying reduced pressure to the underside of the porous sheet material. When the rst valve is opened Patented Dec. 7, 1965 ICC after the porous she'et material has been applied to the supporting means, air is drawn through the porous sheet material. When the second valve is opened after the stencil screen is brought into proximity to the porous sheet material, air is withdrawn from th'e fluid-tight space between the stencil screen and the porous sheet material and the reduced pressure causes a coloring composition disposed on the pervious portions of the stencil screen on the side remote from the porous she'et material to be drawn through the pervious portions of the stencil screen and printing on the porous sheet material. It is highly desirable in carrying out this process to support the porous sheet material on a convex surface so that air pock'ets cannot form in the space between the stencil screen and the porous sheet material as the reduced pressure causes the stencil screen to be drawn into contact with the porous sh'eet material. Inasmuch as the stencil screen is stretched rather tightly in a horizontal plane, the central part will tend to contact the central part of the porous sheet material rst and then gradually and uniformly contact the remainder of the porous sheet material.

In practicing the process the preferred procedure involves placing the porous she'et material on the supporting means, then applying suction from a vacuum pump, or other suitable source, through holes directly beneath the porous sheet material, and applying to the .fporous sheet material by spraying, brushing, or in any other suitable manner, a liquid material in which a predetermin'ed coloring composition or printing ink is at least partially soluble. The liquid or solvent is pulled through the porous sheet material so that itis no longer visible. In the meantime, the stencil screen has been previously prepared having pervious portions corresponding in shape to a predetermined colored configuration which it is desired to print on the porous sheet material and a predetermined supply of coloring composition is applied tothe side of the stencil screen remote from the sheet material. This coloring composition can be any well known heavy concentrated, non-owing printing ink which is sufficiently viscous to remain on top of lthe stencil screen under normal atmospheric conditions but which will llow through the openings in the pervious portions of the stencil scr'een when the pressure on the opposite side of the stencil screen is reduced. The stencil screen containing this coloring composition or printing ink is then brought into proximity to the porous sheet material and a coniined spac'e is formed between the stencil screen and the porous sheet material. A portion of this space extends beyond the edges of the porous sheet material and in this portion of the space openings ar'e provided which are connected to a suitable means for reducing the pressure, such as a vacuum pump. Additionally suction or reduced pressure is applied through these openings to the space between the porous sheet material and the stencil screen thereby causing the coloring composition or printing ink on the remote side of the stencil screen to be pulled through the openings in the pervious portions of the stencil screen onto the porous sheet material. The applied vacuum also pulls the stencil screen into contact throughout the porous sheet material and produces a uniform print on the porous sheet material corresponding to the colors of the color composition on the stencil screen. The suction in the area between the stencil screen land the porous sheet material is th'en discontinued and the pressure allowed to return to normal atmospheric pressure. The stencil screen is thereafter removed from the porous sheet material and the suction is discontinued on the underside Iof the porous sheet material so that the printed material can be removed from the supporting means.

In the embodiment shown in the drawing the supporting means for the porous sheet material consists of an upper base 1 which is curved from side to side and also from front to rear to present a convex surface and a lower base 2 (FIGURE 2) which is also preferably curved in the same manner. These two supporting bases 1 and 2 are separated to provide an air space 3. The bases 1 and 2 are preferably constructed of metal, such as aluminum, but can be made of any other suitable material including rigid plastic materials.

The upper base 1 is provided with a plurality of rather small holes 4 which are uniformly drilled over the entire supporting surface and are on the underside of the porous -sheet material upon which a print or colored configuration is to be applied. Relatively large tapered vacuum holes 5 are provided around the area normally occupied by the porous sheet material. These are connected to a vacuum exhaust passageway 6.

The air-tight separating wall 7 which is made of rubber or other suitable material forms one side of the passageway 6 and another air-tight seal 8 also formed of rubber or other suitable material denes the opposite side of the passageway 6. The sealing Walls 7 and 8 extend on al1 four sides of the printing apparatus. A number of spacers 9, preferably formed of metal or other suitable rigid material, are provided between the two base plates 1 and 2 in order to keep them evenly spaced.

An air seal 10 made of rubber or other suitable material is mounted and sealed to the top of the upper base plate 1 on the outside of the holes 5 and extends upwardly a short distance above the base plate 1 to prevent ingress of air to the space formed when the stencil screen is brought into position in proximity to the porous sheet material to be printed. The sealing wall or strip 19 is preferably formed from closed cell soft sponge rubber.

The lower base plate 2 is mounted on a strong wooden or metal under structure 11 which in turn is fastened to suitable legs or other supporting structure.

The space 3 between the upper base plate 1 and the lower base plate 2 and within the sealing Wall 7 connects to a passageway 12 in a pipe or conduit 13 and the ow of fluid through this passageway is controlled by a valve 14 which is opened and closed by a handle 15 which can be operated automatically in any suitable way. The pipe 13 is connected to a hose or other suitable conduit 16 which in turn is connected to a vacuum pump, not shown.

The space 6 between the inner and outer sealing walls 7 and 8 connects to a passageway 17 in a pipe or conduit 18 controlled by means of a valve 19 operated by a handle 20 or connected to any other suitable operating mechanism, not shown. A hose 21, or other suitable conduit, is connected to the pipe 18 and to a suitable pressure reducing means, such as a vacuum pump. The conduits 16 and 21 may be connected to the same or different vacuum sources. A stencil screen frame 22, which is generally rectangular in shape, supports a stencil screen 23 which is fastened to the frame at the edges and is stretched between the frame in a substantially flat plane as shown. The stencil or printing pattern is applied to the underside of the screen 23 to produce certain areas 24 which are impervious and other areas 2S which are pervious. The color composition 26 to be applied to the porous sheet material is placed over the pervious portions of the stencil screen.

The frame 22 is preferably hinged to a suitable supporting surface by hinges 27 in order to maintain a relatively xed position between the stencil screen and the porous sheet material to be printed. It will be understood, however, that the frame containing the stencil screen may be placed by hand over the porous sheet material to be printed.

The operation of the process in terms of the specific apparatus previously described is as follows. A porous sheet material 28 is placed over the small holes 4 on the supporting base 1. The valve 15 is turned in order to apply suction or vacuum to the passageway 3 thereby holding the sheet material 28 in place and drawing air the stencil screen.

through it. Before or after turning the valve 15 a liquid which is at least a partial solvent for the coloring material, such as, for example, naphtha, mineral spirits, xylene, toluene or benzene, is applied to the upper surface of the porous sheet material 28 by means of a brush, sponge, spray, or in any other suitable manner. The suction removes any excess liquid from the sheet. The stencil screen 24 is brought down upon the strip air seal 10 which prevents outside air from entering the printing space. The printing vacuum is then applied by turning handle 20 of large valve 19 and after a very short period of time, for example, one-half to one second, the valve is turned off again which permits the lifting of the stencil screen. The printed sheet 28 is still held by the suction from passageway 12. When the stencil screen is completely removed from the printed sheet 28 valve handle 15 is turned in order to close valve 14 and thereby discontinue the suction from the underside of the printed sheet. The printed sheet can then be removed from the supporting surface 1. The moisture and solvents in the porous sheet material have been removed under vacuum suction and enough ink or coloring composition has been applied to give a strong printed impression of superior quality.

The coloring compositions 26 may be different and the pervious portions 25 may consist of different designs, letters or other indicia so that the nal printed sheet material can be a multi-colored print produced in a single operation. Successive prints can be made in the same manner without replenishing the supply of coloring material carried by the stencil screen.

Any suitable type of porous sheet material can be used, such as an eighty pound sized paper. In general, it is preferable not to use clay lled papers or other papers which are adversely affected by the application of a solvent. Any conventional heavy printing ink can be employed but the ink should preferably be one which does not dry readily in bulk but dries fast in thin layers from a solvent-treated porous material. Oil base inks can be used in which case the solvent employed to pretreat the porous sheet material would be a solvent such as naphtha, mineral spirits, xylene, toluene or benzene. It will be recognized that the type of solvent may vary depending upon the type of printing ink. For example, with a zein an alcohol solvent would be used. The ink should preferably be one which does not readily oxidize in the air. Various combinations of inks can be used. Heat setting inks can be employed. The pigments employed can be any of the conventional pigments including the well known fluorescent pigments. The printed design can be overprinted with successive screens using different stencils but otherwise applying the same general principles.

It will be seen from the drawing (FIGURE 3) that the passageway 12 leading to the small holes on the under side of the porous sheet material is smaller than the passageway 17 leading to the holes around the perimeter of the sheet material. In general, the amount of suction applied per unit area to the under side of the porous sheet material is less than the amount of suction applied to the printing space between the porous sheet material and Ordinarily approximately twice as much suction is applied to the printing space. This is made possible by the differential in the size of the conduits 13 and 18. Ordinarily, the conduits 16 and 21 are connected to the same vacuum pump. A vacuum of 20 to 28 inches of mercury is usually sufficient. It is desirable that the suction applied to the under side of the porous sheet should be just strong enough to hold the sheet in place and not strong enough to exhaust all of the solvent from the sheet. On the other hand, the suction applied to the printing space should be stronger because of the greater pressure required to pull the printing composition through the previous stencil screen.

The printing colors which are placed on top of the stencil screen over the pervious portions can, if desired,

be enclosed in a boundary Wall made of rubber, metal, or other suitable material, in order to conne them to a predetermined area. This is not always necessary.

The invention is hereby claimed as follows:

1. A process for applying a predetermined colored conguration to a porous sheet material which comprises applying suction to one side of said porous sheet material, applying to the opposite side of said sheet material a liquid in which a predetermined coloring composition is at least partially soluble, thereafter bringing the side of said sheet material to which said liquid was applied into contact with a stencil screen having pervious portions corresponding in shape to said predetermined colored configuration, supplying said predetermined coloring composition to said pervious portions of the side of said screen remote from said sheet material, said coloring composition being a heavy concentrated non-owing printing ink which is suiciently viscous to remain on one side of the stencil screen under normal atmospheric conditions but which will flow through the pervious portions of the stencil screen when the pressure on the opposite side of the stencil screen is reduced, applying additional suction between said stencil screen and said sheet material, 4and continuing to apply said rst named suction and said additional suction for a brief interval until said coloring composition has been drawn through the pervious portion of said screen and printed on the surface of said sheet material.

2. A process as claimed in claim 1 in which the surface of said porous sheet material is a convex surface and the surface of said stencil screen in contact therewith is arched in a curvature following said convex surface.

3. A process as claimed in claim 1 in which the surface of said porous sheet material to which said coloring composition is applied is convexly curved and the surface of said stencil screen is flat prior to contact with said porous sheet material and is arched in a curvature following the convexly curved surface of said porous sheet material upon contact therewith.

4. A process as claimed in claim 1 in which the suction applied to the space between the stencil screen and the porous sheet material is stronger than the suction applied to one side of the porous sheet material.

5. A process for applying a predetermined colored configuration to a porous sheet material which comprises applying suction to one side of said porous sheet material, applying to the opposite side of said sheet material a liquid in which a predetermined coloring composition is at least partially soluble, thereafter bringing the side of said sheet material to which said liquid was applied into contact with a stencil screen having pervious portions corresponding in shape to said predetermined colored configuration, supplying said predetermined coloring composition to said pervious portions of the side of said screen remote from said sheet material, said coloring composition being a heavy concentrated non-flowing printing ink which is suciently viscous to remain on one side of the stencil screen under normal atmospheric conditions but which will flow through the pervious portions of the stencil screen when the pressure on the opposite side of the stencil screen is reduced, applying additional suction between said stencil screen and said sheet material, continuing to apply said rst named suction and said additional suction for a brief interval until said coloring composition has been drawn through the pervious portion of said screen and printed on the surface of said sheet material, discontinuing the application of said additional suction, removing said stencil screen from said sheet material, and thereafter discontinuing said rst suction.

6. A process for applying a predetermined colored con- `figuration to a porous sheet material which comprises supplying a predetermined coloring composition to pervious portions of a taut, flexible, normally at stencil screen, said coloring composition being a heavy concentrated non-flowing printing ink which is suiciently viscous to remain on one side of the stencil screen under normal atmospheric conditions but which will flow through the pervious portions of the stencil screen when the pressure on the opposite side of the stencil screen is reduced, bringing the opposite side of said stencil screen into contact with a conveXly curved porous sheet material, said screen thereby being arched in a curvature following said convexly curved porous sheet material, and drawing said coloring composition through the arched pervious portions of said stencil screen onto the surface of said porous sheet material adjacent said stencil screen solely by the application of suction to the side of said porous sheet material opposite said surface.

7. A process for applying a predetermined color configuration to a sheet material which comprises supplying at least two different coloring compositions of different colors to different pervious portions of a taut, flexible, normally flat stencil screen, said coloring compositions each being a heavy concentrated non-owing printing ink which is suiiciently viscous to remain on one side of the stencil screen under normal atmospheric conditions but which will llow through the pervious portions of the stencil screen when the pressure on the opposite side of the stencil screen is reduced, bringing the opposite side of said stencil screen into arched contact with a convexly curved sheet material to be printed, establishing a predetermined sealed zone of reduced pressure between the stencil screen and the sheet material to be printed around an area to be printed, and reducing the pressure between said stencil screen and said sheet material to be printed in the area to be printed, said reduced pressure of itself being sufficient to cause said coloring compositions to be drawn through the pervious portions of said stencil screen onto the surface of said sheet material.

8. A process as claimed in claim 7 in which said sheet material is porous, and suction is applied to the side of said sheet material opposite the side in contact with the stencil screen adjacent the outer edges of the sheet material, separate suction is applied between the stencil screen and the sheet material in the area to be printed and the application of said first-mentioned suction and said separate suction is continued until said coloring compositions have been drawn through the previous portion of said screen and printed on the surface of said sheet material.

References Cited by the Examiner UNITED STATES PATENTS 737,945 9/1903 Lundeberg. 1,680,500 8/1928 Cotes 101-126 1,922,058 8/ 1933 Miller et al. 101-129 2,239,619 4/1941 Murgatroyd et al. 101-126 X 2,419,694 4/ 1947 Shuttleworth et al. 101--129 2,739,532 3/1956 Fernandez lOl-126 3,129,442 4/1964 Leckie 101--129 X 3,137,230 6/1964 Ichinose lOl-123 X FOREIGN PATENTS 518,036 2/ 1940 Great Britain.

DAVID KLEIN, Primary Examiner. 

1. A PROCESS FOR APPLYING A PREDETERMINED COLORED CONFIGURATION TO A POROUS SHEET MATERIAL WHICH COMPRISES APPLYING SUCTION TO ONE SIDE OF SAID POROUS SHEET MATERIAL, APPLYING TO THE OPPOSITE SIDE OF SAID SHEET MATERIAL A LIQUID IN WHICH A PREDETERMINED COLORING COMPOSITION IS AT LEAST PARTIALLY SOLUBLE, THEREAFTER BRINGING THE SIDE OF SAID SHEET MATERIAL TO WHICH SAID LIQUID WAS APPLIED INTO CONTACT WITH A STENCIL SCREEN HAVING PERVIOUS PORTIONS CORRESPONDING IN SHAPE TO SAID PREDETERMINED COLORED CONFIGURATION, SUPPLYING SAID PREDETERMINED COLORING COMPOSITION TO SAID PERVIOUS PORTIONS OF THE SIDE OF SAID SCREEN REMOTE FROM SAID SHEET MATERIAL, SAID COLORING COMPOSITION BEING A HEAVY CONCENTRATED NON-FLOWING PRINTING INK WHICH IS SUFFICIENTLY VISCOUS TO REMAIN ON ONE SIDE OF THE STENCIL SCREEN UNDER NORMAL ATMOSPHERIC CONDITIONS BUT WHICH WILL FLOW THROUGH THE PERVIOUS PORTIONS OF THE STENCIL SCREEN WHEN THE PRESSURE ON THE OPPOSITE SIDE OF THE STENCIL SCREEN IS REDUCED, APPLYING ADDITIONAL SUCTION BETWEEN SAID STENCIL SCREEN AND SAID SHEET MATERIAL, AND CONTINUING TO APPLY SAID FIRST NAMED SUCTION AND SAID ADDITIONAL SUCTION FOR A BRIEF INTERVAL UNTIL SAID COLORING COMPOSITION HAS BEEN DRAWN THROUGH THE PERVIOUS PORTION OF SAID SCREEN AND PRINTED ON THE SURFACE OF SAID SHEET MATERIAL.
 5. A PROCESS FOR APPLYING A PREDETERMINED COLORED CONFIGURATION TO A POROUS SHEET MATERIAL WHICH COMPRISES APPLYING SUCTION TO ONE SIDE OF SAID POROUS SHEET MATERIAL, APPLYING TO THE OPPOSITE SIDE OF SAID SHEET MATERIAL A LIQUID IN WHICH A PREDETERMINED COLORING COMPOSITION IS AT LEAST PARTIALLY SOLUBLE, THEREAFTER BRINGING THE SIDE OF SAID SHEET MATERIAL TO WHICH SAID LIQID WAS APPLIED INTO CONTACT WITH A STENCIL SCREEN HAVING PERVIOUS PORTIONS CORRESPONDING IN SHAPE TO SAID PREDETERMINED COLORED CONFIGURATION, SUPPLYING SAID PREDETERMINED COLORING COMPOSITION TO SAID PERVIOUS PORTIONS OF THE SIDE OF SAID SCREEN REMOTE FROM SAID SHEET MATERIAL, SAID COLORING COMPOSITION BEING A HEAVY CONCENTRATED NON-FLOWING PRINTING INK WHICH IS SUFFICIENTLY VISCOUS TO REMAIN ON ONE SIDE FO THE STENCIL SCREEN UNDER NORMAL ATMOSPHERIC CONDITIONS BUT WHICH WILL FLOW THROUGH THE PERVIOUS PORTIONS OF THE STENCIL SCREEN WHEN THE PRESSURE ON THE OPPOSITE SIDE OF THE STENCIL SCREEN IS REDUCED, APPLYING ADDITIONAL SUCTION BETWEEN SAID STENCIL SCREEN AND SAID SHEET MATERIAL, CONTINUING TO APPLY SAID FIRST NAMED SUCTION AND SAID ADDITIONAL SUCTION FOR A BRIEF INTERVAL UNTIL SAID COLORING COMPOSITION HAS BEEN DRAWN THROUGH THE PERVIOUS PORTION OF SAID SCREEN AND PRINTED ON THE SURFACE OF SAID SHEET MATERIAL, DISCONTINUING THE APPLICATION OF SAID ADDITIONAL SUCTION, REMOVING SAID STENCIL SCREEN FROM SAID SHEET MATERIAL, AND THEREAFTER DISCONTINUING SAID FIRST SUCTION. 